A conventional radio frequency (RF) switch for switching an antenna over a transmitting circuit and a receiving circuit is descried in Japanese Patent Laid Open No. 7-312568. FIG. 5 illustrates an equivalent circuit of the conventional RF switch. As shown in FIG. 5, a diode 524 is coupled between an antenna 501 and a transmitting circuit 502, and a strip line 540 is coupled between the antenna 501 and a receiving circuit 503. The anode of a diode 546 is coupled to the strip line 540 at the receiving circuit 503 side, and the cathode of the diode 546 is grounded. A control voltage circuit 530 is coupled to the anode of the diode 524.
When a signal is received, namely, when the diodes 524, 546 are both turned off, a capacitor between both ends of the diode 546 decreases a characteristic impedance of the strip line 540 at the receiving circuit 503 side. A compensating capacitor 532 is coupled to the strip line 540 at the antenna 501 side for compensating for the decreasing of the characteristic impedance of the strip line 540.
The compensating capacitor 532 is disposed for the receiving circuit 503. When a signal is transmitted, namely, when the diodes 524, 546 are both turned on, the compensating capacitor 532 becomes an additional capacitor that is added on the signal path between the antenna 501 and the transmitting circuit 502. This increases a loss of the transmitted signal due to inserting the radio frequency switch.